Immune cells can usually be divided into T cells and B cells, wherein the main function of B cells is to secrete various antibodies to protect the body against all kinds of foreign invasion. Bruton tyrosine protein kinase (BTK) is a member of the tyrosine protein kinase subfamily, and belongs to the Tec family kinase. It is mainly expressed in B cells, and distributed in the lymphatic system, hematopoietic and hematological systems. B-cell receptor (BCR) plays a crucial role in regulating the proliferation and survival of various lymphomas selected from subtypes of chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL), mantle cell lymphoma (MCL), and diffuse large B-cell lymphoma (DLBCL). In addition, the effects of B cells in the pathogenesis of rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and other immune diseases have been proven in clinical practice. Bruton tyrosine protein kinase (BTK) is a key protein kinase in the BCR signaling pathway. It is capable of regulating the maturation and differentiation of normal B cells, and is also closely related to various diseases of B cell lymphoid tissue disorders. Therefore, the small molecule inhibitor targeting BTK can be beneficial to the treatment of B-cell malignancies and autoimmune diseases.
Ibrutinib is the first-generation of small molecule inhibitor of BTK developed jointly by Pharmacyclics and Janssen. It was first approved by the FDA for the treatment of mantle cell lymphoma (MCL) in November 2013, and was subsequently approved for the treatment of chronic lymphocytic leukemia (CLL) in February 2014. Ibrutinib binds irreversibly to the cysteine 481 of ATP-binding domain on the BTK kinase through its Michael receptor, thereby inhibiting the downstream signal transmission of BTK, and effectively controlling the growth of tumor cells.
PCT/US14/61393 relates to a compound of formula (I), i.e., (R)-4-amino-1-(1-(but-2-ynoyl)pyrrolidin-3-yl)-3-(4-(2,6-difluorophenoxy)phenyl)-1H-pyrrolo[2,3-d]pyridazin-7(6H)-one. This compound is a novel BTK kinase inhibitor, and has improved kinase selectivity, clinical efficacy or indications, and safety. However, no study was performed on the crystalline form of the compound in this patent application.

The crystal structure of a pharmaceutically active ingredient often affects the chemical stability of the drug. Different crystallization conditions and storage conditions may lead to changes in the crystal structure of the compound, and sometimes accompanying production of other crystal forms. In general, an amorphous drug product does not have a regular crystal structure, and often has other defects, such as poor product stability, finer crystallization, difficult filtration, easy agglomeration, and poor liquidity. Therefore, it is necessary to improve the various properties of the above product. There is a need to find a new crystal form with high purity and good chemical stability.